1. Field of the Invention
Aspects of the present relate to a sealing apparatus. Particularly, the present invention relates to an expandable sealing apparatus. More particularly, the present invention relates to an expandable sealing apparatus for isolating sections of a wellbore.
2. Description of the Related Art
In the oil and gas exploration and production industry, boreholes are drilled through rock formations to gain access to hydrocarbon-bearing formations, to allow the hydrocarbons to be recovered to surface. During drilling of a typical borehole, which may be several thousand feet in length, many different rock formations are encountered.
Rock formations having problematic physical characteristics, such as high permeability, may be encountered during the drilling operation. These formations may cause various problems such as allowing unwanted water or gases to enter the borehole; crossflow between high and low pressure zones; and fluid communication between a highly permeable formation and adjacent formations. In instances where a sub-normal or over-pressured formation is sealed off, the permeability of the formation may be such that high pressure fluids permeate upwardly or downwardly, thereby re-entering the borehole at a different location.
Damage to rock formations during drilling of a borehole may also cause problems for the drilling operation. Damage to the formation may be caused by the pressurized drilling fluid used in the drilling operation. In these situations, drilling fluid may be lost into the formation. Loss of drilling fluid may cause the drilling operation to be halted in order to take remedial action to stabilize the rock formation. Loss of drilling fluid is undesirable because drilling fluids are typically expensive. In many cases, drilling fluids are re-circulated and cleaned for use in subsequent drilling procedures in order to save costs. Therefore, loss of high quantities of drilling fluid is unacceptable.
One method of overcoming these problems involves lining the borehole with a casing. This generally requires suspending the casing from the wellhead and cementing the casing in place, thereby sealing off and isolating the damaged formation. However, running and cementing additional casing strings is a time-consuming and expensive operation.
Furthermore, due to the installation of the casing, the borehole drilled below the casing has a smaller diameter than the sections above it. As the borehole continues to be extended and casing strings added, the inner diameter of the borehole continues to decrease. Because drilling operations are carefully planned, problematic formations unexpectedly encountered may cause the inner diameter of the borehole to be overly restricted when additional casing strings are installed. Although this may be accounted for during planning, it is generally undesired and several such occurrences may cause a reduction in final bore diameter, thereby affecting the future production of hydrocarbons from the well.
Alternatively, inflatable packers may be used to seal off a portion of a wellbore. Typically, the inflatable packer utilizes an inflatable elastomeric bladder to create a fluid seal within the surrounding wellbore or casing. The bladder may be inflated by injecting fluid under pressure into the bladder. In this manner, the bladder is inflated into contact with the wellbore. Typically, the pressure in the bladder is increased to greater than that of the pore pressure of the formation. In this respect, a net seal load is created, thereby sealing off the wellbore.
While the inflatable packer is a viable method of sealing a wellbore, there are potential problems associated with its application. For example, the actuation of the inflatable packer is operated through a complex valve system that may not function properly. Also, like the casing strings, the inflatable packer reduces the inner diameter of the wellbore, thereby potentially limiting the production capacity of the wellbore.
More recently, expandable tubular technology has been developed to install casing strings without significantly decreasing the inner diameter of the wellbore. Generally, expandable technology enables a smaller diameter tubular to pass through a larger diameter tubular, and thereafter be expanded to a larger diameter. In this respect, expandable technology permits the formation of a tubular string having a substantially constant inner diameter, otherwise known as a monobore. Accordingly, monobore wells have a substantially uniform through-bore from the surface casing to the production zones.
A monobore well features each progressive borehole section being cased without a reduction of casing size. The monobore well offers the advantage of being able to start with a much smaller surface casing but still end up with a desired size of production casing. Further, the monobore well provides a more economical and efficient way of completing a well. Because top-hole sizes are reduced, less drilling fluid is required and fewer cuttings are created for cleanup and disposal. Also, a smaller surface casing size simplifies the wellhead design as well as the blow out protectors and risers. Additionally, running expandable liners instead of long casing strings will result in valuable time savings.
Expandable tubular technology has recently been applied to cased hole packers. It has been discovered that expandable packers can be expanded in situ so as to enlarge the inner diameter. This, in turn, enlarges the path through which both fluid and downhole tools may travel. Expandable packers are expanded through the use of a cone-shaped mandrel or by an expansion tool with expandable, fluid actuated members disposed on a body and run into the wellbore on a tubular string. During the expansion operation, the walls of the expandable packer are expanded past their elastic limit. The expandable packer may be expanded against an existing casing to hang a string of casing or seal off an annular area. Consequently, expandable packers allow for the use of larger diameter production tubing, because the conventional slip mechanism and sealing mechanism are eliminated.
An expandable packer is typically run into the wellbore with a running assembly disposed at an end of a drill string. The running assembly generally includes an expansion tool, a swivel, and a running tool. The expansion tool is disposed at the bottom end of the drill string. Next, the swivel is disposed between the expansion tool and the running tool to allow the expansion tool to rotate while the running tool remains stationary. Finally, the running tool is located below the swivel, at the bottom end of the running assembly. The running tool is mechanically attached to the expandable packer through a mechanical holding device.
After the expandable packer is lowered to a predetermined point in the well, the expandable packer is ready to be expanded into contact with the wellbore or casing. Subsequently, the expansion tool is activated when a hydraulic isolation device, like a ball, is circulated down into a seat in the expansion tool. Thereafter, fluid is pumped from the surface of the wellbore down the drill string into the expansion tool. When the fluid pressure builds up to a predetermined level, the expansion tool is activated, thereby starting the expansion operation. During the expansion operation, the swivel allows the expansion tool to rotate while the packer and the running tool remain stationary. After the expandable packer has been expanded against the wellbore or casing, the running assembly is deactivated and removed from the well.
While expanding tubulars in a wellbore offer obvious advantages, there are problems associated with using the technology to create a packer through the expansion of one tubular into a wellbore or another tubular. For example, an expanded packer with no gripping structure on the outer surface has a reduced capacity to support the weight of the entire packer. This is due to a reduced coefficient of friction on the outer surface of the expandable packer. Also, the expandable packer may not expand sufficiently to contact the wellbore and form a seal therewith. More importantly, the expansion of the expandable packer in an open-hole wellbore may result in an ineffective seal between the expanded packer and the surrounding wellbore.
There is a need, therefore, for a packer that will create an effective seal by exerting pressure against a cased wellbore or an open-hole wellbore. There is a further need for a packer that will not reduce the diameter of the wellbore. There is yet a further need for a packer that will expand sufficiently to form a seal with the wellbore.